Background Endovenous laser ablation (EVLA) of the saphenous vein has become one of the preferred treatments for treating saphenous vein reflux that has resulted in symptomatic lower extremity venous insufficiency or varicose veins. This procedure was noted during initial reports to have a low incidence of postoperative thrombosis of the femoral or popliteal vein adjacent to the treated great saphenous vein (GSV) or small saphenous vein (SSV). Later clinical experience suggested that the actual incidence of this event is higher and it was subsequently termed endothermal heat-induced thrombosis (EHIT). Methods We reviewed the office records and the pre- and post-treatment ultrasounds of patients undergoing EVLA in our office from 2005 to 2010 to determine the frequency of EHIT in patients we had treated and then graded them according to a previously published classification. Results There were 528 veins treated in 192 men and 336 women. The clinical, etiology, anatomy, pathophysiology (CEAP) class for these patients was 1 (0), 2 (291), 3 (65), 4 (104), 5 (26), and 6 (40), respectively. The GSV was treated in 496 patients, the SSV in 22, and both were treated in 10 patients. EHIT occurred in 29 of the legs treated for an incidence of 5.1%. The EHIT in the femoral vein were of level 3 (3), 4 (7), 5 (12), and 6 (3), respectively. Two patients developed EHIT in the popliteal vein after EVLA of the SSV. Treatment for the EHIT consisted of observation (13), anticoagulation (9), antiplatelet therapy (2), and nonsteroidal anti-inflammatory agents (1). Duration of therapy was usually 1 week, but 7 patients were treated for periods ranging from 1 to 7 weeks. No pulmonary emboli occurred in any of these patients. The EHIT resolved completely in all patients. Conclusions EHIT after EVLA occurs frequently and mainly consists of low-risk level 3, 4, and 5 deep vein thrombosis. The risk of pulmonary embolism is low and the EHIT typically resolves after 1 week. It can be treated with a short course of antiplatelet or anticoagulation therapy, although observation appears to be sufficient as well for lesser grades of EHIT.